The long-term goal of this project is to further our understanding of the function of retinal glial cells under normal and pathological conditions. This study will focus on the regulation and functions of gap junctions in glial cells of the isolated rat and rabbit retina. The specific aims are (1) to identify the connexin(s) present in retinal astrocytes and Muller cells under normal and pathological conditions using immunofluorescence techniques coupled with confocal microscopy to study the pattern of connexin distribution in glial cells in retinas of normal and RCS rats; (2) to measure electrical coupling between glial cells in the isolated rat and rabbit retinas, and (a) estimate a length constant for the spread of current through the glial network, under control conditions and in retinas exposed to agents (glutamate, dopamine, thrombin) that have been shown to inhibit K+ channels or gap-junctions, (b) determine whether there are gap junctions between mammalian Muller cells, and (c) determine whether astrocyte-to-Muller cell gap junctions are electrically-rectifying as well as chemically-rectifying; ( 3) to identify physiological modulators of gap junctional coupling between retinal glial cells and determine whether these modulators differentially affect homotypic coupling between astrocytes and heterotypic coupling between astrocytes and Muller cells by assessing the effect of tracer spread between retinal glia; (4) to test the hypothesis that (a) intercellular Ca2+ waves are propagated through gap junctions between retinal glial cells, and (b) that Ca2+ waves are propagated via release of a diffusible substance. Alterations in gap junctions can occur under pathological conditions such as nerve transection, epilepsy, and retinal degeneration. The proposed experiments will increase our understanding of how gap junctions between glial cells contribute to retinal function under normal conditions, and in clinical conditions affecting the retina such as glaucoma and diabetic retinopathy.